Battery light

If you release the cap when the car is hot, especially if it is boiling up, there will be heaps of pressure and will continue to be until the water has stopped boiling.. There shouldn't be any pressure when it has all cooled down. Quite often you will get the reverse if you have a small leak i.e. you'll hear the air rushing in when you open the cap on a cold engine

I would say you've got an air lock or blockage .My old car used to do the same till I had the rad replaced .Don,t tempt fate ,it will chuff itself ,so get it flushed .

The plot thickens...

Firstly, there's an aluminum plate riveted to the chassis and front bumper hindering any sight of the rad!

Secondly, after several hours removing the damn thing the radiator looks like it's off a Ford Granada and does not appear to have a drain plug just a top hose!

Finally, i've discovered the fan is stuck solidly onto the outer fan housing and will not turn to save it's life... It must have been like this for a while as it was extremely noisey last month then hasn't made any noise since so I must have been driving fanless for nearly 1000 miles!

Oh bigger...